What is the difference between the various units of turbidity, NTU, FNU, FTU, and FAU? What unit is JTU?
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Dear friends: NTU stands for Nephelometric Turbidity Units; it indicates that the instrument measures the intensity of scattered light at a 90° angle to the incident light. FNU refers to the formaldehyde hydrazine scattering unit, which also indicates that the instrument measures the intensity of the scattered light at an angle of 90° to the incident light. NTU is used in USEPA’s Method 180.1 and the Standard Methods for the Examination of Water and Wastewater. FNU is used for the ISO7027 turbidity method in Europe. After people began to use formazin as a primary standard for turbidity, the FTU, or Formazin Turbidity Unit, came into use. However, this unit is not dedicated to a specific method for measuring sample turbidity. The FAU, or Formazin Attenuation Unit, indicates the degree to which light is attenuated by a sample, as measured by the instrument in a direction at a 180° angle to the incident light. Such measurements are usually carried out using a spectrophotometer or colorimeter, but most regulatory bodies do not recognize this method of measurement. Regardless of the turbidity unit used, whether NTU, FNU, FTU, or FAU, the same formazin standard is employed for calibration. Therefore, when measuring the same formaldehyde hydrazine standard solution, the values expressed in any unit are the same, but when measuring samples, the values expressed in different units can differ significantly. The JTU, or Jackson Turbidity Unit, is a unit that was used in the past; at that time, people visually determined turbidity using a Jackson turbidimeter: the water sample to be tested was poured into a glass tube placed vertically above a flame, until the contents of the tube could no longer be seen. Can they be converted into each other?
I’ve studied it, but I don’t understand analysis and testing
A turbidimeter is a very commonly used instrument for measuring parameters in lightweight and portable water quality analyzers; it should be said that different units are used to express these values depending on the specific samples or testing standards being applied. For example, the turbidity of water samples and that of red wine is expressed in different units. There are also some units that can be converted into each other. For example, 1 ftu = 1 NTU = 0.13 mg/l; it seems there is such a conversion method.
I really don’t know about this. I bought a turbidimeter whose standard solutions are expressed in NTU units. Thank you for sharing the relevant knowledge!
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This post was last edited by qugd on 2022-1-14 at 14:59. The English content on our company’s technical support page below can serve as a useful reference:
Question: What is the difference between the turbidity units NTU, FNU, FTU, and FAU? What is a JTU?
Summary: Turbidity units NTU, FNU, FTU, FAU, and JTU
Answer: NTU stands for Nephelometric Turbidity Unit, indicating that the instrument measures scattered light from the sample at a 90-degree angle to the incident light. FNU stands for Formazin Nephelometric Units, also meaning that the instrument measures scattered light from the sample at a 90-degree angle to the incident light; it is most commonly used in reference to the ISO 7027 (European) turbidity method. NTU is typically used when referring to the USEPA Method 180.1 or the Standard Methods for the Examination of Water and Wastewater. When formazin was first adopted as the primary standard for measuring turbidity, the units FTU or Formazin Turbidity Units were used; however, these units do not specify how the instrument measures the sample. FAU or Formazin Attenuation Units indicate that the instrument measures the decrease in transmitted light through the sample at an angle of 180 degrees to the incident light. This type of measurement is usually carried out using a spectrophotometer or colorimeter, and it is not considered a valid turbidity measurement by most regulatory agencies. A JTU or Jackson Turbidity Unit is a historical unit used when measurements were taken visually using a Jackson Candle Turbidimeter – water was poured into a tube until the flame beneath it could no longer be seen. The turbidity units NTU, FNU, FTU, and FAU are all based on calibrations using the same formazin primary standards; therefore, when a formazin standard is measured, the values for these units will be identical, but the values for samples can vary significantly. FNU stands for Formazin Nephelometric Units; it also indicates that the instrument is measuring the scattered light from the sample, at an angle of 90 degrees to the incident light. FNU is most commonly used as a reference for the ISO 7027 (European) turbidity method. NTU is most commonly used in reference to USEPA Method 180.1 or the standard methods for testing water and wastewater. When carbendazim was first adopted as the primary reference standard for turbidity, the FTU unit or carbendazim turbidity unit was used. However, these units do not explain how the instrument measures the sample. The FAU, or Formazin attenuation unit, indicates the degree of attenuation of the transmitted light passing through the sample, with the transmitted light being 180 degrees out of phase with the incident light, as measured by the instrument. This type of measurement is usually carried out using a spectrophotometer or colorimeter, and most regulatory bodies consider it an ineffective method for measuring turbidity. JTU, or Jackson Turbidity Unit, is a historical unit used for visual measurements with a Jackson candle turbidimeter. Water was poured into a tube until the flame at the bottom of the tube could no longer be seen. The turbidity units NTU, FNU, FTU, and FAU are all calibrated using the same formazin primary standard. Therefore, when the carbendazim standard is measured, the values for these units will be the same, but the values on the samples may vary significantly. The areas with a yellow background and text represent inaccuracies in the translation; note by the author of this post.
Question: What is the difference between the turbidity units NTU, FNU, FTU, and FAU? What is a JTU?
Summary: Turbidity units NTU, FNU, FTU, FAU, and JTU
Answer: NTU stands for Nephelometric Turbidity Unit, indicating that the instrument measures scattered light from the sample at a 90-degree angle to the incident light. FNU stands for Formazin Nephelometric Units, also meaning that the instrument measures scattered light from the sample at a 90-degree angle to the incident light; it is most commonly used in reference to the ISO 7027 (European) turbidity method. NTU is typically used when referring to the USEPA Method 180.1 or the Standard Methods for the Examination of Water and Wastewater. When formazin was first adopted as the primary standard for measuring turbidity, the units FTU or Formazin Turbidity Units were used; however, these units do not specify how the instrument measures the sample. FAU or Formazin Attenuation Units indicate that the instrument measures the decrease in transmitted light through the sample at an angle of 180 degrees to the incident light. This type of measurement is usually carried out using a spectrophotometer or colorimeter, and it is not considered a valid turbidity measurement by most regulatory agencies. A JTU or Jackson Turbidity Unit is a historical unit used when measurements were taken visually using a Jackson Candle Turbidimeter – water was poured into a tube until the flame beneath it could no longer be seen. The turbidity units NTU, FNU, FTU, and FAU are all based on calibrations using the same formazin primary standards; therefore, when a formazin standard is measured, the values for these units will be identical, but the values for samples can vary significantly. FNU stands for Formazin Nephelometric Units; it also indicates that the instrument is measuring the scattered light from the sample, at an angle of 90 degrees to the incident light. FNU is most commonly used as a reference for the ISO 7027 (European) turbidity method. NTU is most commonly used in reference to USEPA Method 180.1 or the standard methods for testing water and wastewater. When carbendazim was first adopted as the primary reference standard for turbidity, the FTU unit or carbendazim turbidity unit was used. However, these units do not explain how the instrument measures the sample. The FAU, or Formazin attenuation unit, indicates the degree of attenuation of the transmitted light passing through the sample, with the transmitted light being 180 degrees out of phase with the incident light, as measured by the instrument. This type of measurement is usually carried out using a spectrophotometer or colorimeter, and most regulatory bodies consider it an ineffective method for measuring turbidity. JTU, or Jackson Turbidity Unit, is a historical unit used for visual measurements with a Jackson candle turbidimeter. Water was poured into a tube until the flame at the bottom of the tube could no longer be seen. The turbidity units NTU, FNU, FTU, and FAU are all calibrated using the same formazin primary standard. Therefore, when the carbendazim standard is measured, the values for these units will be the same, but the values on the samples may vary significantly. The areas with a yellow background and text represent inaccuracies in the translation; note by the author of this post.